1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine that controls a V-type two-cylinder internal combustion engine (hereinafter also referred to as an “engine”) used for a motorcycle for example, and more particularly, it relates to a control apparatus for an internal combustion engine equipped with a failure diagnosis section capable of detecting a piping or tubing disconnection failure of an intake pressure sensor.
2. Description of the Related Art
In general, a control unit (ECU) of a control apparatus for an internal combustion engine drives various kinds of actuators of the engine (injectors, spark plugs, etc.) based on detection information on the various kinds of sensors. The various kinds of sensors of the engine include an intake pressure sensor that measures an intake manifold pressure in an intake system.
For example, in case of a motorcycle, such a kind of intake pressure sensor is arranged, due to the constraint of a mounting space therefor, in such a manner that it is connected to an intake manifold through tubing for measuring an intake manifold pressure (hereinafter also referred to as an intake pressure) therein. Also, the intake pressure sensor is connected to the control unit through a signal line.
In addition, in such a control apparatus for an internal combustion engine, the control unit includes a failure diagnosis section for detecting an abnormality in the signal line, and serves to detect the abnormality of the signal line (an open-circuit failure or a short-circuit failure) connecting between the intake pressure sensor and the control unit based on the amount of change of the intake pressure. Moreover, when the failure diagnosis section detects an abnormality in the signal line, the control unit inhibits the use of the detection information of the intake pressure sensor which has been determined to be abnormal (see, for instance, a first patent document: Japanese patent application laid-open No. 2002-295300.).
However, in the intake pressure sensor with the piping or tubing arrangement as stated above, atmospheric pressure is introduced into the intake pressure sensor if the tubing comes off or is disconnected, so the intake pressure detected in such a case will indicate the same value as that at the time when the engine is stopped (or when a throttle valve is in a full open state).
Accordingly, when there occurs a tubing disconnection failure of the intake pressure sensor, the failure diagnosis section in the above-mentioned conventional apparatus can not detect a signal line abnormality of the intake pressure sensor, but instead makes a determination that the throttle valve is in its full open state. In this case, the control unit controls to supply a large amount of fuel corresponding to the throttle full open state to the engine in spite of the fact that the engine is in its idle state or the throttle valve is in its fully closed state, as a result of which harmful gas components (HC, CO, etc.) in exhaust emissions will be increased.
Further, since an excessive amount of fuel more than necessary is supplied to the engine, an unburnt gas flows into an exhaust pipe, thus generating an afterburning phenomenon thereby to raise the temperature of the exhaust pipe. Furthermore, since the failure (i.e., abnormality in the signal line) is not displayed, there arises a situation where the engine can not be started despite that the user recognizes that the engine is in the normal state.
In the conventional control apparatus for an internal combustion engine, the failure diagnosis section can not detect the tubing disconnection failure of the intake pressure sensor, so there arises a problem that even if a tubing disconnection failure occurs, it is determined that the throttle valve is in its full open state while the intake pressure sensor is in the normal state, thus supplying a large amount of fuel to the engine thereby to cause the deterioration of the exhaust gas or the like.